This was just a project, which had never been implemented due to NKVD reorganization)And on the photograph in your link Beria wears shoulder straps of the Marshal of the Soviet Union, not the mentioned above prototype.

Seems like an insignia from "transitional period" of 1943.When Soviet Army adopted M1943 shoulder insignia Marshal of the USSR had a single star placed in middle of the insignia. Due to the fact that ranks of Marshal and General Comissar of State Security were de-jure equal in USSR, this particular insignia seems like a alpha version.